Proximity-based applications and services represent a fast growing social and technological trend that may have a major impact on evolution of cellular wireless/mobile broadband technologies. These services are based on the awareness of two devices, users, or other communication entities being close to each other and may include such applications as public safety operations, social networking, mobile commerce, advertisement, gaming, vehicle-to-vehicle, etc. Device to device (D2D) discovery within the cellular or long term evolution (LTE) network may be a first step to enable D2D communications service, or may be used to enable other proximity services not involving D2D communication. With direct D2D communication, user equipment (UE) may communicate directly with each other without involvement of a base station or an evolved node B (eNodeB). Device discovery involves discovering one or more other discoverable UEs within discovery range. Device discovery also involves being discovered by one or more other discovering UEs within discovery range.
There are many unresolved issues with respect to device discovery for D2D communication, including resource allocation and signaling, particularly for Proximity Service (ProSe) D2D discovery. One main unresolved issue is that of discovery message size. In designing the discovery message, discovery message size is a critical parameter that largely determines discovery range and resource consumption. The discovery message size dictates the format of the message in terms of number of physical resource blocks (PRBs) and subframes. The issue of discovery message size is one that the standards bodies continue to struggle with.